Faced with a new wave of asylum seekers crossing into Quebec from the United States, the Canadian authorities have opened a temporary welcome center with plenty of space to house them: Montreal’s Olympic Stadium.

Refugees began arriving on Wednesday at the 56,000-seat stadium, where a public hall had been quickly transformed into a shelter with 150 cots and room for hundreds more, as well as internet service, locker room showers and concession stands for preparing food.

The Quebec authorities said the number of asylum seekers crossing into the province skyrocketed in July, when around 1,500 arrived, up from 180 in July 2016.

“We are stretched almost to the limit,” said Francine Dupuis, the spokeswoman for the Quebec government agency responsible for assisting new arrivals.

The refugees are crossing at areas along the international border along Quebec, New York, Vermont and Maine. These are not official border crossings, which means they can skirt a 13-year-old agreement between the United States and Canada requiring asylum seekers to assert their claim in the country they arrive in first.

Under the pact, the Safe Third Country Agreement, those who claim asylum at official border crossings must be denied refuge and sent back. But if they cross at unofficial entry points, the treaty does not apply, and they can seek asylum.

Some refugee advocates in Canada have pressed for the country to pull out of the agreement, saying it encourages people to cross illegally and putsthem in danger. Although Prime Minister Justin Trudeau’s government has resisted these calls, some say that by setting up processing centers at unofficial crossings, arranging for shelter and allowing for refugee claims — exploiting a loophole in the pact — Canada has essentially made the treaty pointless.

“The whole Safe Third Country Agreement doesn’t make any sense, and this is proof of that,” said Mitchell J Goldberg, an immigration lawyer in Montreal.​The Canadian government says it is managing the influx of illegal crossings according to Canadian and international law.

“Trying to slip across the border in this way is against the law and not a ‘free ticket’ into Canada,” Hursh Jaswal, special assistant in the office of the minister of immigration, refugees and citizenship, said in an email. “There are rigorous immigration and customs rules to be followed, and make no mistake, we enforce them to safeguard our communities against security risks.”

He added that the agreement “remains an important tool for Canada and the U.S. to work together on the orderly handling of refugee claims made in our countries.”

More than 4,300 asylum seekers have crossed unofficially into Canada since the beginning of the year, according to government statistics. Over 3,300 of them have crossed in Quebec.

The people who cross at unofficial points of entry like the border with Quebec are arrested by law-enforcement officers and checked for security risks before being given temporary papers and scheduled for refugee claim hearings, immigration officials said.

Around 90 percent of the recent arrivals are Haitians, said Ms. Dupuis of the Quebec agency, Praida, that handles new arrivals. Most go to Montreal, which is home to a large Haitian community.

“They are telling us they’re very uncomfortable staying in the U.S. because they think they will never become legal,” Ms. Dupuis said. “Is this a fear justified? We don’t know.”

In May, President Trump threatened to end a humanitarian program called Temporary Protected Status that allowed 58,000 Haitians to remain in the United States after the devastating 2010 earthquake. That month, John F. Kelly, then the homeland security secretary and now the White House chief of staff, extended the program another six months, through January.

In September 2016, the Obama administration announced it would resume deportations of undocumented Haitian immigrants.

Canada’s location has long limited the number of people arriving by land. The country has selected immigrants through a strict approval process based on skills, education and other requirements intended to best benefit society.

The Canadian authorities say they have sought to bolster law-enforcement and asylum-processing resources at unofficial border crossings to manage public safety. But permitting an influx of asylum seekers as it seeks to enforce the Safe Third Country Agreement has thrust Canada into a delicate diplomatic position with the United States, its neighbor and top trading partner, said Mireille Paquet, an expert on immigration policy at Concordia University in Montreal.

“Canada’s between a rock and a hard place,” she said. “This agreement will not be canceled for the simple reason that doing so would say the U.S. is not safe and produces refugees. The diplomatic implications of that would be tremendous.”